1. Field of the Invention
The present invention relates to electric power generators and, more specifically, to generators that derive power from mechanical contact between surfaces.
2. Description of the Related Art
Wireless, portable and multi-function electronic devices require independent and maintenance-free power sources. The emerging technologies for mechanical energy harvesting are effective and promising approaches for building self-powered systems, because of a great abundance of mechanical energy existing in the environment and the human body. Piezoelectric nanogenerators have been developed to convert tiny-scale mechanical energy into electricity. Another approach to providing power is though triboelectric nanogenerators based on the contact-electrification effect. Triboelectric nanogenerators harvest mechanical energy through a periodic contact and separation of two polymer plates. However, most triboelectric nanogenerators have limited power output.
Energy harvesting by converting ambient energy into electricity may offset the reliance of small portable electronics on traditional power supplies, such as batteries. When long-term operation of a large number of electronic devices in dispersed locations is required, energy harvesting has the advantages of outstanding longevity, relatively little maintenance, minimal disposal and contamination.
When two materials, at least one of which is non-conducting, come into contact with each other, a chemical bond, known as adhesion, is formed between the two materials. Depending on the triboelectric properties of the materials, one material may “capture” some of the electrons from the other material. If the two materials are separated from each other, a charge imbalance will occur. The material that captured the electron will negatively charged and the material that lost an electron will be positively charged. This charge imbalance gives rise to what is sometimes referred to as “static electricity.” The term “static” in this case is somewhat deceptive, as it implies a lack of motion when in reality motion is necessary for charge imbalances to flow. The spark one feels upon touching a door knob is an example of such flow.
The triboelectric effect is a type of contact electrification in which certain materials become electrically charged after they come into contact with another such as through friction. It is the mechanism though which static electricity is generated. The triboelectric effects associated electrostatic phenomena are the most common electrical phenomena in daily life, from walking to driving. However, the triboelectric effect has been largely ignored as an energy source for electricity. Some electrostatic micro-generators have been developed and used in research relating to micro-electro-mechanical systems (MEMS), but such designs rely on an extra voltage source to charge electrode plates instead of harnessing triboelectric effect, leading to complicated structures and fabrication processes.
Previously demonstrated triboelectric generators require periodic contact and vertical separation of two materials that have opposite triboelectric polarities, making it only applicable to harvest energy from intermittent impact or shock. Such systems typically include a cavity with a constantly changing volume, which makes packaging difficult and limits applications in atmospheres with high humidity, corrosive chemicals or gases, and in water or other liquids.
Therefore, there is a need for triboelectric nanogenerators with increased power output.